Disparity tuning is a pervasive property of neurons in almost all visual areas in primate cortex. We will use a novel neuroimaging technique to examine the flow of disparity information from V1 to extra- striate areas in human cortex. This technique relies on source localization using high density EEG coupled to structural and functional MRI anatomical measurements. We will measure the neural response to repetitive changes in disparity in four widely separated cortical areas, V1, V3A, V4 and hMT+ - all known to be important in primate disparity processing. Our first aim examines the sensitivity of the cortical response in these four areas to dynamic random dots, modulated by horizontal or by vertical disparity. We will also explore the response to anti-correlated random dots which are known to drive single units in many cortical areas. Our second aim evaluates the contribution of disparity-modulation to surface segmentation. We will compare the response patterns produced by monocularly modulated changes in figure-ground segmentation to those generated by disparity modulated changes in figure-ground segmentation. Our third aim explores how the loss of stereopsis affects the cortical responses of the strabismic observer. We will specifically look for the cortical locus of strabismic suppression, as well as for the locus of the motion asymmetry that is a defining characteristic of infantile esotropia. PUBLIC HEALTH RELEVANCE Strabismus is a developmental abnormality that affects 3 - 5% of the population, resulting in the loss of stereopsis. The proposed research will measure the cortical response associated with two anomalies of strabismus: strabismic suppression and the motion asymmetry previously observed in VEP measurements. The motion asymmetry is a useful marker for judging the efficacy of treatment, particularly surgery, so understanding its cortical origin will enhance its utility.